A large portion of the chlorine and alkali metal hydroxide produced throughout the world is manufactured in diaphragm-type electrolytic cells wherein the opposed anode and cathode are separated by a fluid permeable diaphragm, usually of asbestos, defining separate anode and cathode compartments. In a typical operation, saturated brine is fed to the anode compartment wherein chlorine is generated at the anode, the brine percolating through the diaphragm into the cathode compartment wherein sodium hydroxide is produced at a concentration within the range of 11 to 18 percent and "contaminated" with large amounts of sodium chloride. This sodium hydroxide must then be concentrated by evaporation and the chloride must be removed to provide a commercial product.
Through the years, substitution of a membrane material for the diaphragm has been proposed. These membranes are substantially impervious to hydraulic flow. In operation, an alkali metal chloride solution is again introduced into the anode compartment wherein chlorine is liberated. Then, in the case of a cation permselective membrane, alkali metal ions are transported across the membrane into the cathode compartment. The concentration of the relatively pure alkali metal hydroxide produced in the cathode compartment is determined by the amount of water added to this compartment, generally from a source exterior the cell. While operation of a membrane cell has many theoretical advantages, its commercial application to the production, for example, of chlorine and caustic has been hindered owing to the low current efficiencies obtained and the often erratic operating characteristics of the cells.